Such systems are described e.g. in U.S. Pat. Nos. 4,171,671 and 4,406,234. As will be observed from these patent specifications, the workpiece holder may take the form of an arrangement of clamps between which various components may be clamped together in the sewing machine in a pre-determined relationship for a `join and sew` operation to be performed thereon. Alternatively so-called pallets may be used in which either a workpiece, in the case of decorative stitching, or a plurality of workpiece components, in the case of a `join and sew` operation, may be clamped in a correct location. One such pallet is described in U.S. Pat. No. 3,988,993.
Whereas pallets successfully serve to hold workpieces in a desired registration (location and orientation) for a sewing operation to be performed thereon, and also have the advantage (as compared with machine clamps) that they can be locked away from the sewing machine so that the machine can continue operating while the next pallet is being loaded, nevertheless the use of pallets in this way (i) gives rise to significant expenditure in terms not only of the initial costs of pallet manufacture but also of storage (in which regard it must be borne in mind that each different type, style and size of workpiece requires its own pallet, except where some compromise between e.g. sizes can be accommodated), (ii) is time-consuming in terms of ensuring that the correct pallet is retrieved from the storage and made available to the operator for the particular workpiece to be sewn, and (iii) is labour-intensive in that for each pallet the workpiece(s) must be loaded into the pallet, the pallet must then be placed in the machine, and at the end of the sewing operation the pallet must first be unloaded from the machine and the finished workpiece then be removed from the pallet.
In the clothing industry, as an alternative to clamping workpieces in pallets a system of belts is used between which workpieces or workpiece components can be held and be advanced into a sewing position, whereafter relative transverse movement is effected between such system and a sewing head to cause a sewing operation to take place on such workpieces (or components). One apparatus including a system of belts operable in this manner is described in GB-A 2 144 777. The purpose of the use of a system of belts in such a case is not, however, concerned with the stitching of complicated patterns on workpieces or the joining of workpiece components together by stitching by effecting relative movement between the workpieces (or components) and the sewing head simultaneously along two co-ordinate axes, but rather merely with initially locating workpieces or components in a desired location and orientation and thereafter sewing them. It does not, therefore, address the problems set out above, which arise from the use of pallets.
It is one of the objects of the present invention to provide an improved automatic sewing machine system in which the use of pallets is dispensed with, while nevertheless enabling a workpiece (or workpiece components) to be held in a known location and orientation for a desired stitch pattern to be sewn thereon by effecting relative movement between the workpiece and a sewing head along two co-ordinate axes under programmed control.